1. Field of the Invention
This invention is related to a design and arrangement of a Common Pilot Channel (CPICH) and a Primary Synchronization Channel (P-SCH) in Evolved Universal Mobile Telecommunications System Terrestrial Radio Access (UTRA).
2. Description of the Related Art
A mobile station (or wireless device) routinely performs a cell search (or synchronization) function to detect and acquire the base stations of a wireless network in the vicinity of the wireless device. Fast detection of the base stations is critical to the performance of both the mobile station and the wireless network, particularly in the new 3rd Generation Partnership Project (3GPP) Evolved UTRA wireless system. Fast detection of base stations allows a mobile station to access a wireless network more rapidly, for instance, by reducing acquisition delay. Fast detection of base stations also enables the mobile station and the wireless network to perform faster handoffs between base station cell sites or between sectors of the same base transceiver subsystem (BTS) of a base station. Additionally, fast detection reduces the number of calls that are dropped during the handoff process.
Correlation procedures are used for a wide range of tasks in a mobile radio receiver. For instance, a receiver receives a signal including data. In a correlation process, the data is compared, in the form of sample values, with a sequence of data items, which are known in the receiver. If the arriving data matches the sequence of known data, a correlation signal is emitted which indicates that the sequence of known data items has been identified in the received signal.
By way of example, time-slot synchronization in the receiver is carried out on the basis of the correlation of a pilot signal with a pilot sequence which is known in the receiver. In a Universal Mobile Telecommunications System (UMTS) Standard, the synchronization signal for the time-slot synchronization is transmitted via a P-SCH (Primary Synchronization Channel). A synchronization sequence, which is known in the receiver, has a length of 256-chip codeword, and is transmitted at a start of each time slot.
Frame synchronization is likewise carried out by correlation of a transmitted pilot signal with a known pilot sequence. In the UMTS Standard, the code sequence for frame synchronization and code group acquisition is transmitted via a S-SCH (Secondary Synchronization Channel). The spreading factor for the second code sequence is likewise 256 chips. A third example of the use of correlation procedures for carrying out a mobile radio task relates to an estimation of a delay time for one transmitted signal propagation path. Owing to multipath propagation in mobile radio systems, one and the same transmitted signal is received with a time offset at the receiver, and with different attenuation levels, via different propagation paths. In the course of an equalization process, the time offset between the individual signal components must be measured and must be compensated for using, for instance, delay estimation. The estimation of the delay time on the propagation path, which is also referred to as delay estimation, is carried out using a product correlation sequence comprising a scrambling code, a channelization code, and pilot symbols.
The time-slot and frame synchronizations are used to search for new (mobile radio) cells in the so-called active set (group of currently used cells) and in a so-called monitor set (group of monitored cells which are candidates for the active set). Time-slot and frame synchronizations must, therefore, be carried out continually even when telephone connection has already been set up. An analogous procedure applies, of course, for delay estimation, which must be continually updated on the basis of changing channel conditions.
A Common Pilot Channel (CPICH) code can be detected directly after Primary Synchronization Channel (P-SCH) detection by correlating all possible pilot sequences with received CPICH. However, the complexity of that procedure may be high due to a long scrambling code (compared to the repetition period of the P-SCH) of, for instance, 10 ms. This implies that, a user equipment (UE) has to deal with the uncertainty of both the scrambling code number and the phase of the scrambling code, which either increases the complexity of the UE or increases the CPICH search time.
In another conventional system, an intermediate step is added between the P-SCH and CPICH detection which uses a Secondary Synchronization Channel (S-SCH). However, conventional systems do no allow for arranging the P-SCH and CPICH in order to make CPICH detection with as much low implementation complexity as possible. A system and method are needed that would allow cell specific scrambling of the CPICH to be applied without the need for the S-SCH.